|Rooney, Alejandro - Alex|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/23/2009
Publication Date: 3/1/2010
Citation: Connor, N., Sikorski, J., Rooney, A.P., Kopac, S., Koeppel, A.F., Burger, A., Cole, S.G., Perry, E.B., Krizanc, D., Field, N.C., Slaton, M., Cohan, F.M. 2010. Ecology of Speciation in the Genus Bacillus. Applied and Environmental Microbiology. 76(5):1349-1358. Interpretive Summary: In this paper, we present the results of a validation study for a method previously described by our group that aims to identify unique groups of ecologically distinct bacteria that potentially represent novel species. Identifying how many such populations exist within a particular clinical or environmental sample is of the utmost importance for agriculture, public health, and human and veterinary medicine, as these distinct populations represent different species that must each be treated with a unique control or monitoring strategy. The results of our study show that the method is robust and capable of detecting novel groups.
Technical Abstract: Microbial ecologists and systematists are challenged to discover the early ecological changes that drive the splitting of one bacterial population into two ecologically distinct populations. We have aimed to identify newly divergent lineages (“ecotypes”) bearing the dynamic properties attributed to species, with the rationale that discovering their ecological differences would reveal the ecological dimensions of speciation. To this end, we have sampled bacteria from the Bacillus subtilis-B. licheniformis clade from sites differing in solar exposure and soil texture, within a Death Valley canyon. Within this clade, we hypothesized ecotype demarcations based on DNA sequence diversity, through analysis of the clade’s evolutionary history by Ecotype Simulation (ES) and AdaptML. Ecotypes so demarcated were found to be significantly different in their associations with solar exposure and soil texture, suggesting that these and covarying environmental parameters are among the dimensions of ecological divergence for newly divergent Bacillus ecotypes. Fatty acid composition appeared to contribute to ecotype differences in temperature adaptation, as those ecotypes with more warm-adapting fatty acids were isolated more frequently from sites with greater solar exposure. In contrast to other bacterial groups where copious ecological diversity is seen within recognized species, the recognized species and subspecies of the B. subtilis-B. licheniformis clade are nearly identical to the ecotypes demarcated by ES, with few exceptions where a recognized taxon is split at most into three putative ecotypes. Nevertheless, the recognized taxa do not appear to encompass the full ecological diversity of the B. subtilis-B. licheniformis clade: ES identified several newly discovered clades as ecotypes that are distinct from any recognized taxon.